EP-A1 0 296 721 disclosed a class of piperidine or 1,2,3,6-terahydropyridine compounds substituted in the 5-position with a five-membered heterocyclic group, including a subclass of optionally substituted 5-tetrazolyl-1,2,3,6-tetrahydro-pyridine compounds. The compounds were disclosed to have high affinity to central cholinergic receptors, in particular high affinity for central muscarinic M.sub.1 receptors, thus being useful in the treatment of Alzheimer's disease, senile dementia, and impaired learning and memory functions.
The structure-activity relationship of this subclass was described by Moltzen et al., J. Med. Chem. 1994, 37, 4085-4099. One of the compounds, i.e. 5-(2-ethyl-2H-tetrazol-5-yl)-1,2,3,6-tetrahydro-1-methylpyridine has been reported to be selective for muscarinic receptors with a several fold higher affinity for M.sub.1 than for M.sub.2 and M.sub.3 receptors (Subtypes of Muscarinic Receptors, The Sixth International Symposium, Nov. 9-12, 1994, Fort Lauderdale). Functionally, it has been described to behave as a partial agonist at M.sub.1 receptors and an antagonist at M.sub.2 and M.sub.3 receptors. Furthermore, the only prominent in vivo effect reported was effect on spatial memory acquisition in young and aged rats, respectively. Recently, the compound was disclosed to show relieving effects after traumatic brain injury, WO 97/17074.
A class of compounds previously reported to show muscarinic effects were described to be useful in the treatment of schizophrenia, cf. WO 9505174 A1 and WO 95/05379.
It has now, surprisingly, been found that the compound 5-(2-ethyl-2H-tetrazol-5-yl)1,2,3,6-tetrahydro-1-methylpyridine shows beneficial effects in the treatment of psychosis, schizophrenia, and schizophreniform diseases.